The three species below have been recorded in the last couple of years.
So, there are 24 species of butterflies occurring in East Lothian. The eleven species mentioned in these last three posts were not recorded here in 1970 and have all apparently appeared here since then. However, as I have now found out, seven of those species did once occur here, as early as the 1800s, but they apparently died out after that.
This of course leaves the big question, why? I certainly can't imagine that the habitat has improved in that time. In fact, the amount of undisturbed space has diminished in that time. I did wonder if it was something to do with the industrial revolution or the use of pesticides, but that wouldn't have made the butterflies head south to more populated areas of the country. Then my wife's cousin cracked it. "What about the Little Ice Age?" she asked. This was something that I hadn't hear of previously.
She sent me some information about the Little Ice Age, and although it isn't unanimously agreed when it began or ended I found some interesting information on Wikipedia. Apparently the NASA Earth Observatory has detected three cold periods starting in 1650, 1770 and 1850. The period of cooling starting around 1850 matches very well with the disappearance of some of these species of butterflies.
That same Wikipedia page also shows a graph of estimated average temperatures, which shows a considerable increase in the last 20 years. This could be a possible reason for the other species extending their range northwards into East Lothian.
I think there are more people recording butterflies these days, but I don't think that is the reason these butterflies have been recorded. Many of the people who send in records have noted new species where they have not seen them before. Possibly some species such as Green Hairstreak and Graylings, which are quite difficult to spot, have been here, undetected for many years.
Of course these are just some initial thoughts and I recognise that there could be some flaws in my theories. I would be very interested to hear other people's opinions about this.
Thomson, G (1980). The Butterflies of Scotland. London: Croon Helm Ltd.
Heath, J (1979). Provisional Atlas of the Insects of the British Isles. Biological Records Centre.